In October 1976, a sodium fluoride (NaF) mouthrinse study was started in Biddeford, Maine, a non-fluoride area. Baseline central examinations (DMFS Index) were made of 825 children in grades 5-7 attending seven schools in the community. Participants were randomly divided into three groups. Under teacher supervision, they rinse either weekly with a 0.2% NaF solution or a 0.1% sodium chloride solution (Placebo) or daily with a 0.05% NaF solution. Treatments are to be carried out for three school years. Follow-up dental examinations are scheduled annually to determine the anti-caries effectiveness of the two fluoride mouthrinse procedures. First year follow-up examinations were made in the fall of 1977. The findings are currently being analyzed.